Preterm birth (PTB) is a significant public health problem and accounts for approximately 11% of all deliveries in the United States. It is the leading cause of prenatal death, and the surviving infants may encounter long-term health problems throughout their lives. The majority of this morbidity and mortality involves a small subset of infants born before 30 to 32 weeks of gestation. Although advancement in medical technology has steadily improved the survival rate of the preterm infants, the PTB rate has not improved during the past 4 decades, showing instead a slight upward trend. Thus, identification of new risk factors for PTB could have significant social and economic impact.
Periodontal disease is one of the newly identified risk factors for PTB. Epidemiologic and intervention studies have indicated a link between these two conditions. However, contradictory reports also exists. The questions of whether periodontal disease is a risk factor for PTB and what is the mechanism underlying the potential link remain. Animal studies have provided evidence supporting the potential link and have suggested two possible mechanisms. One mechanism suggest that periodontal disease could lead to systemic dissemination of inflammatory mediators and/or periodontal pathogens causing adverse pregnancy outcomes. The other mechanism suggests that oral bacteria may translocate specifically into the pregnant uterus and induce adverse pregnancy outcomes due to localized infection.
One of the known causes of PTB is intrauterine infection. The infection rate is inversely related to the gestational age. The paradigm has been that intrauterine infections most commonly originate from the lower genital tract and that the microorganisms invade the pregnant uterus through an ascending mechanism. A less common route of infection is hematogenous transmission, where the infectious organism may originate from other parts of the body. As one of the major microbial habitats in the human body, hosting as many as 700 different species, the oral cavity is a potential microbial reservoir for infection. Indeed, organisms with an oral origin such as Fusobacterium nucleatum and Capnocytophaga spp., have been associated with intrauterine infections, with F. nucleatum being one of the most frequently cultivated from or detected in the infected uterus. However, direct evidence detecting and matching the microorganisms in intrauterine infections with those in the oral cavities of the pregnant women is lacking.